Method for molding a mounting member in place

ABSTRACT

A mounting member is provided with an alignment ring and a plurality of outwardly projecting posts unitary therewith. Each post has a threaded bore for receiving a mounting screw. The member is temporarily releasably secured within a mold with the distal ends of the posts displaced inwardly from an adjacent interior surface of the mold and with the openings of the bores directed towards the adjacent interior mold surface. An article is rotationally molded to encapsulate the member with at least the distal end portion of each post embedded in a formed wall of the article.

This is a division of application Ser. No. 87,219, filed Oct. 22, 1979,now U.S. Pat. No. 4,300,698.

TECHNICAL FIELD

This invention relates to an archorable metal mounting member and to amethod for fabricating an article whereby a molding resin is molded toform a wall with the mounting member embedded as an insert in the wallso that the mounting member can accommodate the attachment of a deviceto the wall of the article.

BACKGROUND OF THE INVENTION

In an article fabricated from molding resins it is sometimes desired toprovide a means for mounting a device to the article. In thoseapplications where the device may impose relatively large forces uponthe molded article, it is frequently necessary to provide a suitablystrong mounting means in the wall of the article to which the device canbe mounted. Further, it is frequently necessary to provide a mountingmeans in the wall that will effect a leak-tight seal with the mounteddevice.

Articles molded from molding resins include hollow, single-piece,unitary tanks manufactured from thermoplastic or thermosetting moldingresins or compounds. Devices, such as fittings, level sendingmechanisms, and the like, may be mounted to the tank and, in some cases,project through the tank wall. Such devices are typically mounted withscrews or bolts to the tank wall.

In the past, in certain applications involving vehicle fuel tanks, amounting structure has been used that includes one or more metal insertsembedded in the tank wall for receiving mounting screws or bolts.Typically, each metal insert is completely embedded in the tank wallexcept for the opening of threaded bores in the insert structure whichcommunicate with the exterior of the tank for receiving the mountingscrews or bolts.

It is important that such metal insert structures be entirelyencapsulated on the inside of the tank to prevent leakage of the tankcontents. In the past, providing a leak-tight assembly around a metalmounting insert structure has been difficult to achieve. This isespecially true in applications where a conventional fuel level sendingunit is mounted to a fuel tank that is subject to vibration (e.g., atank used for gasoline storage or industrial or agricultural equipmentor vehicles).

Today, many fuel tanks for agricultural equipment are rotationallymolded from a thermally cross-linkable high-density polyethylene resin,such as that resin sold under the trade name Marlex CL-100 by thePhillips Chemical Company. It is especially difficult to provide aleak-proof or leak-tight connection of a fuel level sending unit to anembedded, steel insert structure in the wall of such a fuel tank.Conventional steel mounting structures include those of the type with agenerally flat annular ring having threaded bores therein and alsoinclude those of the type with an annular ring having projecting bossesuniformly spaced about the ring with a threaded, blind bore in eachboss. Embodiments of the latter type of mounting structure areillustrated and described in the U.S. Pat. No. 4,023,257 to Wright etal.

As taught by the prior art, the tank wall is molded around the annularring portion of the insert so that the entire ring portion is embeddedin the wall. In the past, it was thought desirable to completely embedor encapsulate the mounting insert, except for the bore openings to theexterior of the tank. However, conventional rotational moldingtechniques with the thermally cross-linkable high-density polyethyleneresins have not consistently produced leak-tight or leak-proofembedments.

The reasons for the failure of prior art mounting inserts to form aleak-proof embedment are believed to involve one or more parameters,such as the mounting insert shape, the mounting insert material, themolding resin compound, and the molding temperature. Although thereasons why conventional inserts frequently leak are not necessarilyfully understood, it is believed that the molding resin does not flowaround the mounting insert as completely as desired during the moldingprocess. Cracks or voids are formed which lead from the tank interior tothe interface between the molding resin and the insert. The voids canthen communicate with the region around the bore openings at theexterior of the tank. This provides leakage paths for the tank contents.Capillary action, of course, can lead to, or add to, leakage throughsuch paths.

It would be desirable to provide a metal mounting insert having aconfiguration adapted to be encapsulated in a molding resin and havingat least portions that are adapted to be embedded in a wall of anarticle molded from the molding resin for subsequently accommodating theattachment of a device to the wall of the article.

Further, it would be desirable to provide a method for molding anarticle with the insert securely embedded therein as a leak-tightassembly. Also, it would be beneficial to provide a mounting insert madeof a material which, when molded in a wall of an article, wouldcontribute to the reduction or elimination of voids at the interfacebetween the molding resin and the insert.

Also, it would be desirable to provide an insert in which threaded borescould be machined and in which the threaded bores would providesufficient strength and resistance to stripping when threadingly engagedwith fasteners for securing a device to the article wall.

SUMMARY OF THE INVENTION

In the preferred embodiment of the mounting insert or member disclosedherein, the member is fabricated as a sand casting of aluminum (e.g.,alloy 319 as listed in Table 1, p. 892, Metals Handbook, 8th Edition,American Society for Metals). The insert includes an alignment ring witha generally annular shape and a plurality of posts unitary with thealignment ring. Each post projects outwardly from the ring and defines athreaded bore for receiving a threaded fastener.

According to the preferred form of the method disclosed herein, theinsert is positioned within a mold cavity and is temporarily, releasablysecured to the mold with the bore openings located adjacent the interiorsurface of the mold but displaced inwardly, or away, from an interiorsurface of the mold. If necessary, the bores are initially plugged toprevent flow of the molding resin therein. Preferably, the article isrotationally molded with a thermally cross-linkable high-densitypolyethylene, such as the product sold under the trade name MarlexCL-100 by Phillips Chemical Company.

During the rotational molding process, the article wall forms around thedistal end portion of each post so that the distal end portion of eachpost is effectively embedded in the article wall. The insert's alignmentring, being displaced further away from the mold interior surface, isnot embedded in the formed article wall. However, during the rotationalmolding process, the alignment ring and portions of the posts that arenot embedded in the wall are nevertheless completely encapsulated withthe molding material. Subsequently the molding resin is allowed to atleast partially solidify and then the article, with the now embeddedinsert, is released from the mold.

With the structure and method described above, it has been found that aleak-proof or leak-tight assembly is readily and consistently formed.The formation of voids or other leakage paths at the interface betweenthe molding material and the metal insert is virtually eliminated.

The reasons why the leakage paths are virtually eliminated with thisstructure and method are not necessarily completely understood, andthere is no intent herein to be bound by any theory or by anyexplanation. However, it is believed that the use of certain materials,such as aluminum, instead of the steel compositions used in the priorart structures, permits the mounting structure to rapidly heat up,during the molding process, to a temperature close to that of themolding resin. This prevents localized cooling of the molding resin asit flows in contact with the mounting insert. It is believed thatlocalized cooling can lead to poor or incomplete flow of the moldingmaterial around the insert and can contribute to the formation of voidsand other leakage paths at the interface between the molding materialand mounting structure. If the metal insert has approximately the sametemperature as the molding material, this tendency is reduced, if noteliminated altogether.

Further, it is believed that the configuration of the mountinginsert--wherein the annular alignment ring is displaced away from thearticle wall--provides a number of advantages over the prior art insertsin which the entire insert, including any ring configuration, is whollyembedded within the article wall. Specifically, with the novel insertdisclosed herein, the problem of encapsulating both the top and bottomof an alignment ring completely within the article wall is totallyeliminated. Thus, the article wall can be more easily and consistentlymolded to a uniform thickness.

Further, the positioning of the alignment ring away from the articlewall necessarily removes a large metal mass from within the wall andthus eliminates the large heat sink effect of this metal mass from thecritical wall region. Thus, the wall region can be molded without havingto design for or otherwise accommodate the effect of a large heat sinkin the molding process.

With the preferred embodiment of the insert as formed of sand castaluminum, it has been found that the bores in the posts may be threadedfor receiving mounting screws or bolts of a device to be secured to thetank wall and that the threads in the posts provide a surprisinglystrong threaded connection. For typical uses wherein a fuel levelsending unit is secured with bolts to the posts in a fuel tank wall, thethreaded connections are surprisingly resistant to stripping, even whensteel bolts are used. Thus, the novel mounting structure disclosedherein can provide an extremely strong, as well as leak-proof,connection of a device to a wall of an article molded from a moldingresin.

Numerous other advantages and features of the present invention willbecome readily apparent from the following detailed description of theinvention and embodiments thereof, from the claims, and from theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming part of this specification, and inwhich like numerals are employed to designate like parts throughout thesame,

FIG. 1 is a fragmentary, partially broken away perspective view of awall of a tank molded from a molding resin and having a metal mountingmember embedded therein;

FIG. 2 is a perspective view of the top of the novel mounting memberdescribed herein;

FIG. 3 is a fragmentary, partially broken away perspective view of themounting member of FIG. 2 as fabricated in a tank molded from a moldingresin and showing portions of the mounting member embedded in the tankwall with unembedded portions of the mounting member encapsulated by themolding resin;

FIG. 4 is a top plan view of another embodiment of the novel mountingmember illustrated in FIG. 2;

FIG. 5 is an elevational view of the embodiment of the mounting memberillustrated in FIG. 4; and

FIG. 6 is a simplified schematic diagram showing the location of fourmounting members in two fuel tanks molded from a molding resin andconnected with a conduit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention may be used in many different forms. There are shown inthe drawings and will herein be described in detail preferredembodiments of the invention. It should be understood, however, that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention and is not intended to limit the inventionto the embodiments illustrated.

The precise shapes and sizes of the components herein described are notessential to the invention unless otherwise indicated, since theinvention is described with reference to illustrative embodimentsthereof.

It will be understood that references made herein, and in the claims, tovarious terms such as "metal" and "molding resins" are illustrative. Theterm "metal" is used herein to include single elements as well ascompounds and alloys. The term "molding resin" is used herein toinclude, among other things, thermoplastic and thermal settingsynthetic, hardenable resins.

For ease of description, the mounting member or insert structure will bedescribed in a position in the top horizontal wall of a fuel tank. Itwill be understood, however, that the mounting member may bemanufactured, stored, transported, used, and sold in an orientationother than the position described.

The choice of materials for the fabrication of the mounting member andof the article molded around the mounting member is dependent, in part,upon the particular application involved and upon other variables, asthose skilled in the art will appreciate.

The novel mounting member described herein is particularly adapted forbeing encapsulated with molding resin and for being at least partiallyembedded in the wall of an article formed from such molding resin.Techniques for molding resins are well known in the art, and theconventional molding process details that are unrelated to thepositioning of the mounting member in the mold are unimportant to thepresent invention.

The novel mounting member disclosed herein is especially well suited forbeing embedded as an insert in a wall of an article that is rotationallymolded from a thermally cross-linkable high-density polyethylene resinpowder, such as that sold under the trade name Marlex CL-100 by PhillipsChemical Company.

Rotational molding techniques are well known in the art and therotational molding process details that are unrelated to the positioningof the mounting member in the mold are unimportant to the presentinvention. In general, rotational molding techniques are disclosed inthe aforementioned U.S. Pat. No. 4,023,257 and in Plastics EngineeringHandbook of the Society of the Plastics Industry, Inc., ed., JoelFrados, Van Nostrand Reinhold Ltd., (New York, N.Y., 1976), PP. 348 etseq.

FIG. 1 illustrates the wall 10 of a hollow article, such as a fuel tank,molded about a ring-like mounting member or insert 14 so that themounting member 14 is entirely embedded within the wall 10. The priorart mounting member 14 is made of steel and has bores 16 equally spacedaround the member. Each bore 16 extends completely through the memberand is internally threaded to receive a screw or bolt. The wall 10 maybe molded with an internal aperture 18 having a generally cylindricalconfiguration concentric with the ring mounting member 14.Alternatively, the wall 10 may be first molded without an aperture andthe aperture 18 may be subsequently drilled or cut into the wall 10.

The bores 16 are typically plugged during the molding process so thatthey are exposed, at one end, to the exterior surface of the wall 10. Itis to be noted that the wall 10 completely surrounds the ring-likemounting member 14, except for the regions directly over each bore 16.

A fitting or device, such as a fuel level sending unit (notillustrated), may be mounted to the wall 10 by means of bolts or screwsthreadingly engaged with the bores 16. If a conventional fuel levelsending unit is thus mounted, a portion of the unit is received withinthe aperture 18 and projects through the wall 10 to the interior of thetank.

In those situations where the mounting ring 14 is embedded within a wall10 of a fuel tank, the fuel tank is typically fabricated as a one-piece,hollow tank by means of conventional rotational molding techniquesgenerally described in the U.S. Pat. No. 4,023,257 and in the PlasticsEngineering Handbook of the Society of Plastics Industry, Inc. citedabove.

To fabricate the assembly illustrated in FIG. 1, the ring mountingmember 14 can be first bolted or otherwise releasably attached to theinterior cavity walls of a conventional rotational mold prior tocharging the mold cavity with the molding resin. To this end, bolts maybe secured through the mold wall to the bores 16. The mounting bolts arepositioned in relation to the mold wall so that the mounting ring 14 isspaced inwardly of the interior surface of the mold to permit thedesired thickness of the molding material to be molded between themounting member 14 and the interior surface of the mold.

Following the proper positioning and securement of the mounting member14 inside the mold, the mold cavity is charged with the molding resin ormaterial and the conventional rotational molding sequence is effected toform the wall 10 on the interior surface of the mold cavity and tothereby embed the mounting member 14 within the formed wall 10.

Where mounting members of the type illustrated in FIG. 1 are used tomount fuel level sending units in fuel tanks that have been rotationallymolded from a thermally cross-linkable high-density polyethylene resin,it has been found that the encapsulation of the mounting members are notalways entirely leak-proof or leak-tight. In fact, cracks or voids, suchas at 22, frequently form in the wall 10 during the molding process andprovide a leakage path from the interior of the tank through the wall tothe wall/insert interface. The fuel tank contents, such as gasoline,flows because of, or with the aid of, capillary action through the void22 and along the interface between the wall 10 and the mounting member14 to the bores 16 from which the fuel then leaks to the exterior of thetank.

Although not completely understood, it is believed that the voids 22form for a number of reasons. First, it is believed that the molding ofthe wall 10 completely around the annular ring mounting member structurecannot be effectively accomplished because the mounting member 14physically impedes the flow of molding resin around the member. Also,because the thickness of that portion of the wall defined between thewall surface and the mounting member 14 is relatively thin. Thus, theflow of molding resin between the interior surface of the mold cavityand the mounting member 14 is restricted. This barrier to the flow ofthe molding resin can prevent effective leak-tight encapsulation of themounting member.

In addition, since the ring-like mounting member 14 presents astructural mass of steel embedded entirely within the wall 10, it actsas a heat sink and causes a localized cooling of the flowing moldingresin as the resin comes in contact with the mounting member. Thepremature, localized cooling is undesirable and is thought to lead tothe formation of cracks and voids and otherwise contribute toinsufficient encapsulation of the ring-like member. Other types of priorart steel mounting inserts having ring-like structures entirely embeddedin the wall of the molded tank are also believed to suffer from theseeffects and the resulting tendency to leak.

The exact mechanisms by which voids are formed and the exact mechanismswhich account for the poor encapsulation of the mounting member may notbe completely understood and there is no intent herein to be bound byany theory or by any explanation as provided above.

In order to overcome the above-discussed leakage problems associatedwith certain mounting member structures known to the prior art, a novelmounting member 28 is provided as illustrated in FIG. 2. The mountingmember 28 is preferably sand cast from aluminum (e.g., alloy 319 aslisted in Table 1, p. 892, Metals Handbook, 8th Edition, AmericanSociety for Metals), through other metals or alloys, including brass orzinc, may be used in some applications. Also, in some applications, themounting member may be fabricated with permanent molding techniques orwith die casting techniques.

The member 28 has a generally annular alignment ring 30, the exteriorand interior periphery of which each define a generally cylindricalsurface, and has a plurality of posts 34 unitary with the alignment ring30. Each post projects upwardly or outwardly from the ring 30 anddefines a threaded blind bore 40 for receiving a threaded fastener. Ofcourse, the bore 40 is typically threaded by conventional means afterthe mounting member 28 has been sand cast.

The alignment ring 30 functions to connect the mounting posts 34 in apredetermined array as a one-piece, unitary assembly. This offers anadvantage over prior art mounting members that require welding or othersecuring techniques to provide mounting screw receiving posts in apredetermined array. Further, this has an obvious advantage over othertypes of prior art structures in which a separate, individual mountingmember is associated with each mounting screw and wherein each separatemounting member must be individually retained in place within a moldduring the molding process. The use of a single, unitary member 28eliminates handling of multiple parts and reduces the time required forplacement in the mold.

The mounting member 28 is particularly well suited for being embedded asan insert in the wall of an article molded from a molded resin,especially from a thermally cross-linkable high-density polyethyleneresin powder such as that sold under the trade name Marlex CL-100 byPhillips Chemical Company. As illustrated best in FIG. 3, the mountingmember 28 is preferably embedded in the molded wall 50 of an article,such as a fuel tank, with the alignment ring 30 disposed outwardly fromthe wall 50. Only the distal end portions of the posts 34 are embeddedwithin the wall 50. The wall 50 is molded with apertures 52 in theregions over the post bores 40 to provide access thereto so thatmounting screws or bolts may be threadingly engaged with the posts 34.As can be seen in FIG. 3, the entire mounting member 28 is encapsulatedwith the molding resin so that leakage from the interior tank iseffectively prevented.

A central aperture 54 may be molded in the article wall 50 concentricwith the mounting member 28 or may be subsequently drilled or cut intothe wall after molding.

Preferably, the alignment ring 30 is displaced away from the wall 50 soas not to interfere with the formation of the wall 50 during the moldingprocess. The alignment ring is spaced from the article wall so thatspaces are defined between the alignment ring and the wall between theposts. Thus, during the molding sequence, the flow of molding resin isnot blocked or impeded by the alignment ring 30. This is in contrastwith prior art mounting members, such as that illustrated in FIG. 1,where the ring-like structure is embedded entirely within the wall ofthe molded article and necessarily acts as a barrier to impede the flowof molding resin during the formation of the wall.

According to one form of the method, the novel mounting member ispreferably embedded in an article by means of molding the article from athermally crosslinkable high-density polyethylene resin powder, such asthat sold under the trade name Marlex CL-100 by Phillips ChemicalCompany, with conventional rotation molding techniques. The methodspecifically includes positioning the mounting member in a mold cavitywithin a mold and temporarily releasably securing the mounting member tothe mold. The mounting member is positioned in the mold so that thedistal ends of the posts and bore openings are displaced inwardly fromthe interior surface of the mold. The member 28 is oriented so that thealignment ring portion 30 is positioned further from the interior moldsurface than the distal ends of the posts 34. Typically, the mountingmember is secured within the mold by means of bolts or screws passingthrough the mold wall and threadingly engaged with the post bores. Thosebores, if any, that are not bolted to the mold are plugged, as withsuitable screws or unthreaded plugs, to prevent flow of the moldingresin therein during the molding process.

To mold the article, the mold is charged in the conventional manner withthe thermally cross-linkable high-density polyethylene resin powder andthe rotational molding sequence is initiated. During the rotationalmolding, the mounting member is preferably encapsulated with at leastthe distal end portion of each post embedded in a formed wall of thearticle and with the alignment ring displaced away from the formedarticle wall.

After the article has been molded, the molded resin is permitted to atleast partially solidify and the formed article, with the embeddedmounting member therein, is then removed from the mold. To this end, thereleasably secured mounting screws are threadingly disengaged from themounting member bores. Also, any plugs that had been threadingly engagedwith the bores to prevent flow of the molding resin into the bores wouldbe removed.

The rotational mold used in the manner described above may include asolid, generally cylindrical, inwardly projecting mold portion aboutwhich the mounting member could be concentrically disposed to permitmolding of the article with an opening in the article wall to provideaccess through the mounting member. This would provide an accessaperture similar to the access aperture 54 illustrated for the articlewall 50 in FIG. 3, and can be generally of the type shown in U.S. Pat.No. 4,023,257. Alternatively, the article wall could be molded withoutsuch a central aperture and the aperture could be subsequently drilledor otherwise machined into the article at the appropriate location.

Fuel tanks are typical of articles molded in this manner, and aresulting molded fuel tank structure would be that illustrated in FIG.3. It is to be noted that the alignment ring, though preferablydisplaced away from the tank wall, is, in any case, entirelyencapsulated with the molding resin.

Another embodiment of the mounting member is illustrated in FIGS. 4 and5 and is designated generally therein by numeral 70. In contrast withthe embodiment illustrated in FIG. 2, the embodiment 70 in FIGS. 4 and 5has an alignment ring 71 with a generally cylindrical inner surface 72and has scalloped, concave exterior surface regions 74. Posts 80 areintegrally formed as a unitary part of the alignment ring 71 andfunction in the same manner as the posts 34 illustrated for theembodiment in FIG. 2. This form of the mounting ring is particularlywell suited for those applications in fuel tanks wherein the circularcylindrical surface 72, after encapsulation, is intended to function asa restraining guide for an inwardly projecting portion of a device to bemounted to the fuel tank.

FIG. 6 schematically illustrates a novel assembly of two tanks, uppertank 90 and lower tank 92, which are adapted to hold fuel inagricultural equipment or vehicles. The tanks 90 and 92 are connectedwith a flexible conduit 94. The conduit 94 may be connected withappropriate fittings (not illustrated) to the tanks by means of thenovel mounting members disclosed herein (e.g., member 70 in FIG. 4) andwhich are schematically illustrated in dashed line in FIG. 6 at 96 and98. Additionally, fuel level sending units may be mounted to each tankwith the novel mounting member as designated generally at 102 for tank90 in FIG. 6 and at 104 for tank 92 in FIG. 6.

The novel mounting member disclosed herein may also be made inrelatively large diameters for use as a leak-proof seal mounting aroundlarge openings in articles, such as filler neck openings in fertilizertanks. Rotationally molded fertilizer tanks are presently made incapacities from 25 to 1400 gallons. The novel mounting member disclosedherein, if provided in a nominal size of 20 inches in diameter, could beused in the filler necks of the largest of these tanks. Also, the novelmounting member disclosed herein may be used at agitator rod openingsand at the spray tube manifold connection.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the true spirit andscope of the novel concept of the invention. It is to be understood thatno limitation with respect to the specific apparatus illustrated hereinis intended or should be inferred. It is, of course, intended to coverby the appended claims all such modifications as fall within the scopeof the claims.

It is claimed:
 1. The method for fabricating an article molded from a molding resin having a wall with a mounting member embedded as an insert wherein, upon completion of the molding step, said mounting member can accommodate the attachment of a device to the wall of the article, said method comprising the steps of:providing a mounting member having an alignment ring with a plurality of posts unitary with the ring, each post projecting outwardly from said ring and having a distal end defining a threaded bore for receiving a threaded fastener; positioning said mounting member within the cavity of a mold and temporarily releasably securing said mounting member to said mold with the openings of said bores facing an interior surface of the mold; molding said article to form a wall of the article in which is embedded at least a portion of each said post with at least said threaded bore of each said post communicating with the exterior of said article, with said alignment ring being spaced from said formed wall, and with said alignment ring being encapsulated with said molding resin along with any portions of said posts extending from said formed wall to said alignment ring; permitting said resin to at least partially solidify; and releasing said mounting member and article from said mold.
 2. The method in accordance with claim 1 in which said step of providing said mounting member includes providing a mounting member of sand cast aluminum.
 3. The method in accordance with claim 1 in which said step of molding includes the step of charging said mold with a thermally cross-linkable high-density polyethylene resin powder and the step of subsequently rotationally molding said article.
 4. The method in accordance with claim 1 in which said step of molding said article includes rotationally molding said article.
 5. The method in accordance with claim 1 including the further step of providing a solid, generally cylindrical, inwardly projecting mold portion and in which said step of positioning said mounting member includes positioning said mounting member with said posts circumferentially disposed about said inwardly projecting mold portion to thereby permit the molding of said article with an opening in said article wall to provide access through said mounting member.
 6. The method in accordance with claim 5 in which said step of positioning said mounting member includes positioning the mounting member with the distal end of each said post displaced inwardly from an interior surface of said mold and in which the method includes the step of plugging any open bores in said posts to prevent the flow of molding resin therein and to permit communication through the formed wall between said bores and the exterior of the article. 